His first novel was The Hypocrite: A Novel of Oxford and London Life, published anonymously in 1898. From 1900, he was engaged in writing fiction, producing about 125 novels in the succeeding years. The most famous was When It Was Dark, which reached sales of 500,000 copies.[3] The book describes the attempt by a Jew, the malevolent Constantine Schaube, to overthrow the whole of the Christian world by fraudulently disproving the Resurrection.

After its publication, the Bishop of London preached about When It Was Dark at Westminster Abbey. Calling it "a remarkable work of fiction" he said it depicts how the world would be if the Resurrection were proved to be a gigantic fraud. ". . .you feel the darkness creeping round the world, you see . . . crime and violence increase in every part of the world. When you see how darkness settles down upon the human spirit, regarding the Christian record as a fable, then you quit with something like adequate thanksgiving, and thank God it is light because of the awful darkness when it was dark."[4]

When It Was Dark has been criticised for its stereotyping of Jews and their portrayal as intent on destroying what Thorne viewed as the most valuable element of British life - the Christian faith and the spiritual values associated with it.[5] Other critics have also labeled the book as anti-Semitic.[6]

Thorne's sequel titled When It Was Light (1906), was not published under his name and repeated the plot to disprove the resurrection of Christ but it lacked the public impact of the earlier work. It revealed again Thorne's fears regarding an urban-inspired threat of spiritual and moral degeneracy.[7]

Thorne was a prolific author of horror and mystery novels which sometimes have a redeeming bizarreness.[8] His novels include: Made in His Image (1906), The Soul-Stealer (1906), The Angel (1908), Not in Israel (dedicated to Cecil Broadhurst (1913), And it Came to Pass (1915), The Secret Sea-Plane (1915), The Enemies of England (1915), Lucky Mr Loder (1918), The Secret Monitor (1918), The Air Pirate (1919), Doris Moore (1919), The House of Danger (1920), The City in the Clouds (1921), The Love Hater (1921), The Dark Dominion (1923) and When the World Reeled (1924). He also wrote numerous essays and a biography of Frederick Nicholas Charrington (1850–1936), the English social reformer who devoted his life to Temperance work.[9]

Thorne was a close friend of the publisher Leonard Smithers and a friend of the poet Ernest Dowson.[10] He was known for his heavy drinking. Who's Who 1906 listed his recreations as shooting and French literature, and his address as Trink, Lelant, Cornwall.